The ease with which a tire becomes unseated (leaves its rim seat) and then detaches from the rim when its inflation pressure decreases and a transverse force is applied to the tire is one of the tire features that is important to the safety of the passengers of a vehicle fitted with tires. The standardization organizations have therefore set out target values to be obtained (such as in Chinese standard GB/T 2978-2008, for example) and corresponding test methods (such as the method recommended in Chinese standard GB/T 4502-2009, for example). One example of a test method is also described in patent U.S. Pat. No. 3,662,597, whereby a conical form is applied to a sidewall of the tire, then the pressure applied to the sidewall is increased and the sidewall movement is recorded. A similar test method has been adopted in NHTSA (National Highway Traffic Safety Administration, the American Federal Road Safety Organization) Federal Motor Vehicle Safety Standard No. 109.
Most tires designed for sporty road driving have a relatively short sidewall height, and this places them at a disadvantage in unseating tests. The increasingly demanding recommendations laid down by the standardization organizations are creating the need to make these tires even more resistant to unseating and rolling off.
In theory, the resistance to unseating could be increased by bonding the tire to the mounting rim, but this solution has the disadvantage of making the tire very difficult to unmount. It might also be possible to modify the geometry of the rim to make unseating more difficult, but this approach would entail destandardization.